Urban rat populations are rising in many of the world’s major cities, a trend researchers at the University of Richmond in Virginia link to global warming.<br><br>Analyzing data from 13 U.S. cities as well as Tokyo, Amsterdam and Toronto, they found rat numbers increased the most in cities that have warmed the fastest. San Francisco, Toronto, New York, Amsterdam and Washington, D.C., saw the highest growth.<br><br>The researchers suggest that securing food waste to limit the pests’ access to it is the most effective way to curb rat populations.<div></div><br>